Fuel evaporative control systems are typically used in automobiles to prevent fuel tank vapors from entering the atmosphere. Fuel vapors are typically generated when fuel is introduced into a fuel tank, or when fuel sloshes or splashes in a fuel tank as a result of road conditions or vibrations, or operator driving dynamics.
Contained within the evaporative control systems are carbon canisters. The carbon canisters trap fuel vapor when an engine is not running. The canisters are filled with activated charcoal granules that are capable of adsorbing fuel vapors.
When the engine of an automobile is running, the intake manifold vacuum acts on the charcoal canister purge line. This causes fresh air to flow through the filter and into the canister. The fresh air picks up the stored fuel vapors and carries them through a fuel vapor line. The vapors enter the intake manifold and are introduced into the combustion chambers for ignition with injected fuel.
Typically, as described above, carbon canisters are filled with pelletized or granular carbon. Pressure is applied against a bed compression plate, using a coil or spring leaf spring or springs to maintain carbon bed integrity, as the bed tends to compact during its useful life. Molded-in spring posts are typically used to hold the springs or coils within the canister.
One problem with typical carbon canister constructions is that the carbon canisters are made of molded plastic and the bed compression plates are made of of metal. Due to the difference in materials, the canister and plate expand and contract at different rates, creating the possibility that the carbon granules or pellets may leak.
Another problem with typical carbon canister constructions is that the molded-in spring posts are difficult to manufacture. These posts are difficult to mold into acceptable shapes and sizes, and also require long cure cycle times.
Further, the current designs of carbon canisters require a complicated support structure to maintain the carbon bed integrity. Springs, such as a strip leaf spring, or coils welded to the bottom of the bed apply pressure to the bed compression plates to maintain carbon bed integrity, as the bed tends to compact during its useful life.
It is thus highly desirable to limit or eliminate carbon pellet leakage resulting from expansion or contraction of the carbon canister relative to the bed compression plate.
It is also highly desirable, from a design and manufacturing standpoint, to simplify the design of the carbon canister systems by eliminating molded-in spring posts and to limit the amount of parts used for maintaining carbon bed integrity.